The invention relates as indicated to trolleys for target ranges, and to target ranges provided with such trolleys.
Trolleys which carry target mechanisms for moving targets, especially targets adapted to be moved from an inoperative or concealed position to an operative or exposed shooting position are known. One disadvantage with many such prior trolleys is that it is difficult to camouflage the track and the trolleys in such a way that the trolleys can move to "sneak-up" to a desired position before the target is moved to the operative or exposed shooting position, thereby simulating a surprise attack, without the shooter being able to anticipate where the target is likely to appear, or to conceal the combination of the track and the trolley so that when the target carried by the trolley is, for example, a representation of a tank, the tank appears to move realistically over the ground.
It has been proposed previously to provide a trolley that moves on a mono-rail type track, a trolley of this type being described in British patent specification No. 1,367,752. The trolley described in that Specification is provided with a generally rectangular housing which is supported by two co-aligned drive wheels, one at each end of the housing, which rotate in a vertical plane, the drive wheels being mounted on the uppermost rail of a mono-rail type track which track comprises two rods or tubes which are parallel to one another and located one above the other, the rods or tubes being interconnected by vertical webs at spaced intervals. It will be appreciated that this type of track is relatively narrow and is thus easier to conceal than the conventional track formed of two parallel rails mounted on sleepers. The wheels that are mounted on top of the track are used to drive the trolley, and jockey wheels are provided which engage the lowermost rod or tube of the track to maintain the trolley in a vertical orientation.
Certain disadvantages have been experienced in connection with the trolley described in British patent specification No. 1,367,752. The wheels used to drive the trolley have been provided with a recess in the periphery thereof, so that a relatively large surface of the wheel contacts the tube. This has been found to be necessary to enable the trolley to move successfully along rails which are inclined to the horizontal, and rails which are wet or damp. Also, to improve the traction of the trolley the periphery of the driving wheels has been formed from a material having a high coefficient of friction to ensure that there is a good grip between the wheels and the track. It has been found that, as a result of this combination of features, if a trolley is caused to negotiate a bend in the track it is possible that the side edges of the recess formed in the drive wheels will engage the edge of the track, and instead of the trolley negotiating the bend the foremost drive wheel will ride up the track. This possibility arises since one side edge of the recess will engage the side of the track with a high co-efficient of friction, and the trolley will maintain its linear motion causing the wheel to ride up the track. Thus the trolley may become derailed. Although such de-railments are an infrequent occurrence, the possibility of such de-railments occurring is a disadvantage of the prior proposed trolley. De-railments of the type described above occur most frequently when the trolley is carrying a large erected target and a wind is blowing transversely to the direction of movement of the trolley, since the effect of the wind is to urge the drive wheels firmly into engagement with the rail, thus resisting the tendency of the trolley to turn when the track is curved. Thus, reduced speed specifications are necessary.
A further disadvantage of the apparatus described in British patent specification No. 1,367,752 results from locating the driving wheels above the uppermost rail. For example, the housing of the trolley extends for a substantial distance above the level of the uppermost rail of the mono-rail type track requiring relatively large earth banks or the like in order to conceal the trolley. Moreover, large diameter drive wheels which might otherwise increase top speed capabilities are not possible without increasing the overall height of the trolley housing. This is undesirable since it makes concealment of the trolley more difficult.
Another disadvantage of the trolley described in British patent specification No. 1,367,752 stems from the utilization of a single mechanical, friction-type braking system which operates only on the drive wheels. Since the braking action is not directly applied to the rail itself, there is no assistance in maintaining the vertical orientation of the trolley during braking so as to withstand the deleterious effects of sideways loading. Further, the components of the brake system experience considerable wear during operation and therefore require periodic maintenance and replacement. It has also been found that traction is lost if the wheels lock-up when braking the trolley along downwardly inclined rails, or rails that are damp or wet. As a result, the brake system described in the British reference is not particularly adapted for high speeds.